1. Field of the Invention
The present invention relates to a communications system and method, and particularly to a communications system and method which emulate connectionless LAN environments on a connection-oriented transport network and automatically assign them to end stations.
2. Description of the Related Art
Asynchronous Transfer Mode (ATM) is a promising technology for multimedia data communications, which offers a range of transmission rates and different qualities of service to efficiently handle various types of I/O traffic over a single network medium, such as data, audio, and video. ATM, a cell-based transport mechanism, enables end stations to communicate through a pre-established path called a virtual channel, and hence is connection oriented. In contrast to this, existing local area networks (LANs) use connectionless protocols and broadcast functions, which cannot guarantee the bandwidth and quality of service required for delivery of realtime audio and video information. Since it is beneficial to combine those technologies, ATM-LAN systems have been developed. This ATM-LAN emulates LAN services across an ATM transport system, realizing more cost-effective and seamless network connections for existing and future LAN applications.
The ATM Forum""s LAN Emulation (LANE) specifications Ver 1.0 and 2.0 define the mechanisms to use the vast base of existing LAN applications on an ATM transport system. The LANE emulates network services at the Media Access Control (MAC) layer.
Typically, existing LAN stations are designed to operate on the Ethernet. Because of the lack of a direct ATM access capability, most LAN stations are attached to the ATM network via appropriate ATM hubs or routers having ATM interface. In the LANE terminology, those ATM hubs and routers are referred to as the xe2x80x9cLAN emulation clientsxe2x80x9d (LECs). LAN stations exchange messages with their local LECs, using well-known Ethernet protocols, while the LECs communicate with their peer LECs over an ATM network, according to message formats defined in the LANE specifications. Those LECs provides the LAN end stations with seamless connections, so that LAN applications can be integrated transparently with the ATM network.
FIG. 14 shows the configuration of an ATM network with LAN emulation capabilities. A group of LAN end stations (xe2x80x9cstationsxe2x80x9d for short) 2a to 2c are connected to their nearest ATM hub 200, while another group of stations 3a to 3c to another ATM hub 300. The ATM hubs 200 and 300 are linked with each other via a xe2x80x9ccloudxe2x80x9d of switched connection services provided by ATM switching facilities (ATM-SW) 600. This ATM connection service cloud is also coupled to the following LANE elements: a LAN Emulation Configuration Server (LECS) 100, LAN Emulation Servers (LES) 400-1 and 400-2, and Broadcast and Unknown Servers (BUS) 500-1 and 500-2.
The above-listed network elements operate as follows. The ATM switching facilities 600 provide end-to-end switched connectivity for multiple users, with the ATM technologies. The LECS 100 is a server which provides LANE clients with the address of the most appropriate LES and maintains a database of the resultant associations. When joining the network, every LEC (i.e., two ATM hubs in the present case) first turns to the LECS 100, sending a configuration request message requesting information about which LES should be used. The LECS 100 responds to this request by assigning an appropriate LES to the requesting LEC and sending back the ATM address of that LES. The LESs 400-1 and 400-2 provide address resolution services in two emulated LAN environments, which are logically defined on the same ATM network. The BUSs 500-1 and 500-2 support broadcast traffic over the emulated LAN environments. The ATM hubs 200 and 300 are multiport devices accommodating a plurality of LAN stations, the ports of which can be logically assigned to different LAN segments (or broadcast domain), each group of stations forming a separate emulated LAN (ELAN). Two LAN environments are realized in this way, independently of the physical locations of their end stations.
The illustrated system provides two ELANs, which are distinguished by their ELAN-IDs (or ELAN names), ELAN-1 and ELAN-2. Ports on the two ATM hubs 200 and 300 are assigned those ELAN-IDs as shown in the lower half of FIG. 14. That is, the ports #1 and #2 on the ATM hub 200 and the same on the ATM hub 300 are for the first ELAN environment, ELAN-1. This assignment allows the stations 2a, 2b, 3a, and 3b to communicate with each other within the domain of ELAN-1. On the other hand, the ports #3 and #4 on the ATM hub 200 and the same on the ATM hub 300 are for the second ELAN environment, ELAN-2. This allows the stations 2c and 3c to communicate with each other within the domain of ELAN-2. The LES 400-1 and BUS 500-1 are dedicated to ELAN-1, and the LES 400-2 and BUS 500-2 to ELAN-2.
Conventional ATM hubs, however, require manual set-up operations so that appropriate ELAN-IDs will be assigned to their ports. If the port setup conflicts with the operating parameters of the station being connected, the ATM hub cannot work correctly with that station. Suppose, for example, that the user has relocated the station 2a from port #1 to port #3 on the ATM hub 200. In this case, the station 2a can no longer work as a member of ELAN-1, since the port #3 is assigned to ELAN-2. To make the station operate correctly, he/she has to modify the current setup of the ATM hub. This is indeed a burdensome task, particularly for corporate users of ATM-LAN systems. For those users, relocation of LAN stations from one office floor to another is not an unusual event because their organizations tend to change dynamically to remain competitive. In the case that a separate ELAN is deployed for each organizational unit, frequent relocation of stations could impose increased workloads on the network administrators since they have to redefine the ELAN-ID setups of ATM hubs. For this reason, there has been a need for more flexible and easy-to-use ELAN systems.
Taking the above into consideration, an object of the present invention is to provide a communications system which automatically assign an appropriate ELAN-ID to each attached end station, whichever hub port is used to physically accommodate the station.
Further, another object of the present invention is to provide a communication method which constructs emulated LAN environments on a connection-oriented network.
To accomplish the first object, according to the present invention, there is provided a communications system which constructs emulated LAN environments on a connection-oriented network. This system comprises the following elements: (a) a plurality of LAN stations each having an identifier; (b) a LAN emulation server employed in each emulated LAN environment to provide address resolution services thereon, each LAN emulation server having a network address (ATM address) on the connection-oriented network; (c) a broadcast server employed in each emulated LAN environment to support broadcast traffic thereon; (d) a LAN emulation configuration server; and (f) a LAN emulation client coupled to at least one of the LAN stations. Here, the LAN emulation configuration server comprises an ATM address manager which manages associations between the identifiers of the LAN stations and the ATM addresses of the LAN emulation servers, and when a specific identifier is given, determining which ATM address is relevant to the given identifier. Further, the LAN emulation client comprises the following elements: an ATM address requesting unit which requests the LAN emulation configuration server to provide the ATM address of the LAN emulation servers, as well as requests the LAN emulation servers to provide the ATM address of the broadcast servers associated therewith; an ELAN configuration database which stores operating parameters for the emulated LAN environments, including the identifiers of the LAN stations, the ATM addresses obtained in response to the request from the ATM address manager, and information about connections; and a data communication unit which transfers data according to the parameters stored in the ELAN configuration database.
To accomplish the second object described above, according to the present invention, there is provided a communication method which provides emulated LAN environments constructed on a connection-oriented network. This method comprises the following steps: (a) at a LAN emulation configuration server, managing associations between identifiers of LAN stations and ATM addresses of LAN emulation servers supporting the individual emulated LAN environments; (b) sending a request message from a LAN emulation client to the LAN emulation configuration server, the request message containing the identifier of a specific LAN station to request the ATM address of a LAN emulation server that is relevant to the LAN station; (c) sending an address request message from the LAN emulation client to the relevant LAN emulation server, so as to obtain the ATM address of a broadcast server supporting the emulated LAN environment to which the specific LAN station belongs; (d) storing operating parameters in the LAN emulation client, which include the ATM addresses returned in response to the request message sent at the step (b) and the address request message sent at the step (c), and information about network connections established to reach the LAN emulation server and broadcast server; and (d) conducting a communication session between the LAN stations within the emulated LAN environment, according to the stored operating parameters.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.